[PATCH v4] rockchip: board: Increase rng-seed size to make it sufficient for modern Linux

[Dragan Simic]

Hello Alex,

On 2024-10-15 00:15, Alex Shumsky wrote:
> Increase rng-seed size to make Linux happy and initialize rng pool 
> instantly.
> Linux 5.19+ requires 32 bytes of entropy to initialize random pool, but 
> u-boot
> currently provides only 8 bytes.
> Linux 5.18 and probably some versions before it used to require 64 
> bytes.
> Bump min value to 64 bytes to be on a safe side.
> 
> Boot with 8 byte rng-seed (Linux 6.11):
>     # dmesg | grep crng
>     [   12.089286] random: crng init done
> Boot with 32 byte rng-seed (Linux 6.11):
>     # dmesg | grep crng
>     [    0.000000] random: crng init done
> 
> Linux source references:
> https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/drivers/char/random.c?h=v5.19#n551
> https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/drivers/char/random.c?h=v5.18#n236
> 
> Signed-off-by: Alex Shumsky <alexthreed at gmail.com>
> Fixes: d2048bafae40 ("rockchip: board: Add board_rng_seed() for all
> Rockchip devices")
> Reviewed-by: Dragan Simic <dsimic at manjaro.org>
> ---
> 
> Changes in v4:
> - fix typos and code style

The v4 is looking good, thanks!

> Changes in v3:
> - reword warning
> - increase default rng_seed_size to support older linux as well
> - reword commit message
> 
> Changes in v2:
> - add env config knob rng_seed_size
> - add warning for small rng_seed_size
> - 12-character commit SHA in Fixes
> 
>  arch/arm/mach-rockchip/board.c | 11 ++++++++++-
>  1 file changed, 10 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/arm/mach-rockchip/board.c 
> b/arch/arm/mach-rockchip/board.c
> index 3fadf7e412..ca6404776f 100644
> --- a/arch/arm/mach-rockchip/board.c
> +++ b/arch/arm/mach-rockchip/board.c
> @@ -472,9 +472,18 @@ __weak int misc_init_r(void)
>  __weak int board_rng_seed(struct abuf *buf)
>  {
>  	struct udevice *dev;
> -	size_t len = 0x8;
> +	ulong len = env_get_ulong("rng_seed_size", 10, 64);
>  	u64 *data;
> 
> +	if (len < 64) {
> +		/*
> +		 * rng_seed_size should be at least 32 bytes for Linux 5.19+,
> +		 * or 64 for older Linux kernel versions
> +		 */
> +		log_warning("Value for rng_seed_size too low (%lu) and likely
> insufficient for the Linux RNG initialization\n",
> +			    len);
> +	}
> +
>  	data = malloc(len);
>  	if (!data) {
>  		printf("Out of memory\n");